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Causation is not easily derived from observational (non-experimental) data but a strong case for the plausibility of vaccines effectiveness in reducing hospitalisation and mortality rates is clearly visible in Portuguese epidemiological data. The number of cases is in a growing trend since October 2021 and is currently about 3 times higher than it was one year ago.

Interestingly, the number of hospitalisations and deaths did not increase proportionally since July 2021. Before the Ómicron variant, in October 2021 there was a growing number of cases identified in the population similar to the same period one year ago and still a much lower number of hospitalisations and deaths occurred. Regardless of the variants, the decreasing trends in hospitalisations and deaths rates proportionally to the number of cases is clear since July 2021.

There may be many different explanations for such trends, but the fact that Portugal has a vaccination rate above 80% of the population, since October 2021, is clearly a plausible justification for the reduction of the number of hospitalisations and deaths since them.

The impact of vaccines in the reduction of transmissibility rates may not be clearly established and it is known that vaccines don’t fully prevent the occurrence of Covid-19, however data clearly suggests that they are effective in boosting immunity, reducing severe disease occurrence and reducing hospitalisations and deaths rates. This is good news.